1. Field of the Invention
The present invention relates to an organic photoelectric semiconductor device and a method for manufacturing the same and, more particularly, to an organic photoelectric semiconductor device including quaternary group VA salts in an organic salt-containing layer and a method for manufacturing the same.
2. Description of Related Art
Organic photoelectric semiconductor devices, such as small molecule organic light-emitting diodes (OLEDs), polymer light-emitting diodes (PLEDs), magnetic small molecule organic light-emitting diodes, magnetic polymer light-emitting diodes, small molecule organic solar cells, polymer solar cells, magnetic molecule organic solar cells, magnetic polymer solar cells etc., have attracted considerable attention due to their potential advantages such as flexibility, lightweight and low fabrication cost over their inorganic counterparts. Among organic photoelectric semiconductor devices, organic light-emitting diodes (e.g. small molecule organic light-emitting diodes, polymer light-emitting diodes, magnetic small molecule organic light-emitting diodes, magnetic polymer light-emitting diodes) and organic solar cells (e.g. small molecule organic solar cells, polymer solar cells, magnetic molecule organic solar cells, magnetic polymer solar cells) are particularly interesting owning to the increasing demand for new renewable energies and numerous advantages of organic light-emitting diodes, such as wide viewing angles, low manufacturing cost, high response rate (one hundred times or more faster than that of LCD), low power consumption, good adaptability for DC driving model in portable electronic products, light weight, miniaturization facility, high picture contrast, and high brightness.
In organic photoelectric semiconductor devices, an organic active layer of organic small molecules or polymer molecules is sandwiched between a cathode and an anode. Accordingly, while applying an electric field on an organic photoelectric semiconductor device capable of converting electricity into light (e.g. organic light-emitting diodes), electrons and holes would be respectively injected from the cathode and the anode, and transmitted to the organic active layer, resulting in recombination of electrons and holes and thus emission of light. On the contrary, electrons and holes are generated in an inner part of an organic photoelectric semiconductor device capable of converting light into electricity (e.g. organic solar cells) under illumination, and the generated electrons and holes are transferred to the cathode and the anode, respectively, by the action of internal electric fields. Then, the electrons generated therein would flow out to an external circuit through the cathode, to generate an electric current.
Organic photovoltaic (OPV) technology is still in the early stages of development. Despite the advantages that it already has or may have in the future, the efficiency is still very low compared to the conventional PVs. Thereby, the performance enhancement of OPVs is absolutely necessary if organic solar cells are to dominate the future solar cell market. One important key to high performance organic solar cells is the selection of the electron collecting layer. The purpose of the electron collecting layer is to provide hole blocking capability and a low resistive pathway for efficient electron extraction.
Regarding organic light-emitting diodes, in consideration of conductivity and low interfacial barrier between the organic active layer and the anode/cathode, low-work-function (low-WF) metals and high-work-function (high WF) metals may be used as the cathode and the anode, respectively, to promote the injection of electrons and holes respectively into LUMO and HOMO of the organic active layer. Among them, calcium (Ca), magnesium (Mg), barium (Ba) and lithium (Li) are commonly used low-WF metals. However, these metals have high reactivity and are susceptible to oxidation with moisture and oxygen in air, resulting in the deterioration of electrodes and reduction of electroluminescence (EL) efficiency. In order to overcome the above-mentioned problems, it is desirable to use an environmentally stable metal, such as Al, Ag, or Au. However, these environmentally stable metals have high work function. To overcome injection barrier for electrons and promote electron injection to the organic active layer, the following approaches were suggested: (1) forming an alloy by co-plating various low-WF metals and anti-corrosion metals as the cathode, such as Mg/Ag alloy or Li/Al alloy; and (2) inserting an electron injection layer between the organic active layer and the high-WF metal to reduce the electron-injection barrier and to promote the injection of electrons from the cathode into the organic active layer, resulting in the enhancement of electron-hole recombination.
Many excellent materials with efficient electron-injection ability have been suggested, including: (a) alkali metal compounds, which are commonly applied to an electron injection layer, e.g. metal acetates (CH3COOM, M=Li, Na, K, Rb or Cs), metal fluorides (MF, M=Li, Na, K, Rb or Cs), lithium oxide (Li2O), lithium metaborate (LiBO2), potassiumsilicate (K2SiO3), or cesium carbonate (Cs2CO3); (b) oxygen-containing polymers or surfactants, e.g. poly(ethylene glycol) (PEG) doped in emissive organic polymer materials, or a modification layer of neutral surfactants (CmH2m+1(OCkH2k)nOH) or poly(ethylene oxide) (PEO) to modify the interface between the organic active layer and the Al electrode; (c) ionic polymers appliable to polymer light-emitting diodes, e.g. sodium sulfonated polystyrene (SSPS); (d) metal oxides having a conduction band between about 3.8 eV and 4.3 eV and applicable to PLEDs, which provide higher electron mobility than hole mobility to thereby confine holes to the organic active layer and to enhance the recombination, e.g. n-type semiconductor materials (TiO2, ZnO etc.); and (e) ionic conjugated polymers, which can enhance the electron-injection efficiency and improve the EL intensity of devices, e.g. poly(fluorene)-based conjugated polymers.
However, the above-mentioned electron-injection materials have drawbacks, including: (I) these materials only work well with Al and thus the choice of the cathode metal is limited; (2) synthesis difficulty of partial materials causes the reduction of yield and high manufacturing cost; and (3) these materials cannot be applied to both a solution fabrication process and a dry process, and thus the application is restricted.